The present invention relates generally to a method of sterilization for micro-isolators, a device used to house laboratory animals, especially rodents. The invention further relates to the apparatus used in performing this sterilization cycle.
In the medical industry rodents, especially mice, are used in studies of drugs and toxicology, in which harmful side effects are observed before exposing such drugs to humans. In order to insure accurate data collection in such studies, laboratory animals must be free of contamination, and must not be exposed to any foreign bacteria or viruses. These precautions are necessary to keep the number of variables at a minimum.
In order to ensure that lab mice are free of contamination, they must live their entire lives in an environment isolated from foreign microorganisms. Lab mice are born under aseptic conditions, and they must be housed in such a sterile environment from birth until death.
As can be seen in FIG. 1, lab mice 13 are housed in a micro-isolator 10 a clear plastic cage which includes a housing 11 and a lid 12 formed with a ventilation grid, formed of a plastic mesh which includes spun-bonded polyester fabric filter paper. This filter paper permits air and humidity to freely pass between the mice and the outside environment. However, the filter paper has a mesh that filters the air down to 0.2 microns, thus preventing the admission of microorganisms, which are much larger. The micro-isolator receives and retains the essential necessities needed to maintain the mice 13, including bedding 14, and a rack 15, which supports and retains food 16 and a sipper bottle 17, which is filled with a predetermined volume of water.
Mice, contained in the micro-isolators, are maintained in a sterile environment at all times to insure isolation against outside contaminants. Nevertheless, the micro-isolator must be cleaned once or twice a week in order to provide a clean living environment for the mice. Accordingly, the mice must be transferred from the dirty micro-isolator to a fresh sterile micro-isolator, in which freshly sterilized bedding, food and sipper bottle with water have been provided.
In the prior art, the assembly of a fresh micro-isolator was a time-consuming and labor-intensive process. The micro-isolator unit itself, along with the bedding, food and sipper bottle, each had to be individually sterilized. In preparation for the lab mice, the micro-isolator and its sterilized components had to be manually assembled in a clean room environment, in a chamber with laminar air flow, in order to insure that the sterilized components were not recontaminated prior to use.
The preparation of micro-isolators must be done on-site. The maintenance of a clean room and the human resources required for this purpose adds considerable expense to the preparation of sterile microisolators. Considering that some institutions process as many as 7000 micro-isolators a week, the expense of such microisolators can add up quickly. Consequently, an apparatus and method which would permit faster preparation of sterilized micro-isolators, using less manpower, would be a very desirable advance in the art.
Some prior art practitioners have contemplated sterilizing an assembled micro-isolator, with bedding, food and sipper bottle deposited therein, prior to sterilization. However, such a procedure has presented several problems. In order to achieve efficacious sterilization, steam must be injected at temperatures of between 118.degree.-130.degree. C. These are temperatures of moist heat which are sufficient to destroy foreign micro organisms. At such temperatures, the water in the sipper bottle will boil at atmospheric pressure. Should the sipper bottle be permitted to boil over, the micro-isolator and its contents will be wetted, and the sipper bottle will end up nearly dry. Such conditions do not provide an acceptable environment for laboratory mice. Thus, sipper bottles have needed to be sterilized separately from the rest of the micro-isolator, in order to guard against boil over and the resulting saturation of the bedding.
Sterilization temperatures are typically achieved using a steam charge which leaves residual condensed moisture on the micro-isolator and its contents. The unit may be dried by reducing the chamber pressure to a subatmospheric level, which permits the rapid evaporation of any condensed moisture. However, such a reduction in pressure also causes the water in the sipper bottle to boil. As a result, the sipper bottles would boil over and saturate the bedding at this stage as well. This and other difficulties encountered in the prior art are overcome by the present invention.